As one of a series of papers related to thermodynamics and phase equilibrium for the "Salt Lake Brine System", the present paper deals Li-divided by,Na+,K+,Mg2+/Cl-,SO42--H2O. In order to describe thermodynamics and phase equilibrium of the title system, the Pitzer ion interaction model of aqueous electrolyte was applied. In addition to Pitzer parameters for single electrolytes for the entire range of concentration up to the saturation. the mixing parameters for pairwise ions including ion Li+, such as (Li+, Na+), (Li+, K+), (Li+. Mg2+), for triple ions (Li+. Na+. Cl-), (Li+, Na+, SO42-),... and (Cl, SO42-, Li+) etc are also needed. We managed to obtain reasonable Pitzer parameters for single electrolytes and the osmotic coefficient of LiCl-NaCl-H2O solutions were determined in our lab. All our data together with those published were fitted to acquire the needed parameters. The model has been extended to the system including ion Ca2+ in our recent work. As one of a series of papers related to thermodynamics and phase equilibrium for the "Salt Lake Brine System", the present paper deals Li-divided by,Na+,K+,Mg2+/Cl-,SO42--H2O. In order to describe thermodynamics and phase equilibrium of the title system, the Pitzer ion interaction model of aqueous electrolyte was applied. In addition to Pitzer parameters for single electrolytes for the entire range of concentration up to the saturation. the mixing parameters for pairwise ions including ion Li+, such as (Li+, Na+), (Li+, K+), (Li+. Mg2+), for triple ions (Li+. Na+. Cl-), (Li+, Na+, SO42-),... and (Cl, SO42-, Li+) etc are also needed. We managed to obtain reasonable Pitzer parameters for single electrolytes and the osmotic coefficient of LiCl-NaCl-H2O solutions were determined in our lab. All our data together with those published were fitted to acquire the needed parameters. The model has been extended to the system including ion Ca2+ in our recent work.